Method of making glass tube envelopes



L. M. POLAN 2,697,311

METHOD OF MAKING GLASS TUBE .ENVELOPES Dec. 21, 1954 Filed Dec. 19, 1949 2 Sheets-Sheet 1 EINVBNWI'ON kivumiw 3 o! cum Dec. 21, 1954 L. M. POLAN 2,697,311

METHOD OF MAKING GLASS TUBE ENVELOPES Filed Dec. 19. 1949 2 Sheets-Sheet 2 United States Patent' METHOD OF MAKING GLASS TUBE ENVELOPES Lincoln M. Polan, Huntington, W. Va., assignor, by mes'ne assignments, to Polan Industries Incorporated, a corporation of West Virginia Application December 19, 1949, Serial No. 133,717

3 Claims. (Cl. 49--82) The present invention pertains generally to electron discharge tubes. More specifically, the invention relates to a novel glass envelope for such a tube and to a method of making the envelope, finding particular but by no means exclusive utility in the construction of cathode ray tubes for television equipment.

Heretofore, it has been a common practice to make cathode ray tube envelopes of blown glass. Although this operation involves considerable skill and expense, it has been considered reasonably satisfactory for tubes of relatively small diameter. The rapid advance of the electronic art, particularly in the television field, has

been accompanied by a demand for substantial quantities of larger sized tubes. By the same token, the de 'mand also increased for tubes of higher strength and better optical qualities in their window panel areas.

ripheral skirt integral therewith and adapted to be fused to the tube funnel. To secure thenecessary stiffening in the window panel, the central portion is' thickened progressively toward the skirt and over an annular area of substantial width. Such marginal thickening of the central portion of the window panel produces a prismatic effect upon the light passing therethrough. Consequently,

the light rays passing through the thickened area are bent out of parallelism and toward the effective base of the prism, or in other words, toward the peripheral edge of 'the window panel. The net effect of this phenomenon -i to produce an optical distortion knownl in the art as -rings of confusion The distortion becomes increasingly apparent as the observer moves away. from a posi- 'tion squarely in line with the center of the window panel. Not only does this prismatic effect cut down the maximum viewing area on the window panel, but in addition, it drastically reduces the angle from which an undistorted picture may be viewed on the panel.

A further disadvantage of the thickened window panel constructiondescribed above is a substantial increase in the weight of the tube. This is highly undesirable in tubes constructed for commercial television receivers.

, To overcome certain of the foregoing disadvantages,

'those skilled in the art have-recognized the desirability of constructing a tube envelope having a ground and polished window panel of substantially uniform thickness. Work in that direction has, however, been confined heretofore to tubes with metal funnels. This cons'truct'ion introduces further disadvantages peculiar to itself such, for example, as the need for specially insulated mountings when the tubesare used in an ordinary television set; I Accordingly, one object of the invention is to provide a novel glass envelope for cathode ray tubes and the like havinga ground and polishedwindow panel withsub- ,stantially more undistorted viewing area than-the window pane! of a comparable glass envelope'made according to mfilh ds, Pre a ste s-i. i

Another object is to provide a glass tube envelope of the character set forth and which will possess substan tially greater strength than envelopes of comparable size heretofore produced.

A further object is to provide a tube envelope of the above type which will be susceptible of economical manufacture.

Another object is to provide a novel method for manufacturing tube envelopes of the type set forth and which involves the effecting of an unusually strong seal between the window panel and the funnel member.

A further object is to provide a method of the foregoing character which will be susceptible of use on a mass productive scale with a minimum of spoilage and without the necessity for skilled operators.

Other objects and advantages of the invention will become apparent from the following detailed description, taken in connection with the accompanying drawings, wherein:

Figure 1 is a perspective view of an illustrative tube envelope embodying the present invention and manufactured in accordance with the method thereof.

Fig. 2 is an enlarged fragmentary sectional view taken igngiiudinally through the illustrative tube envelope of Fig. 3 is a further enlarged fragmentary sectional view through the seal between the panel and the tunnel of the tube envelope as shown in Fig. 2.

Fig. 4 is a longitudinal sectional view through the panel and the funnel of the illustrative tube envelope prior to the fusion operation.

Figs. 5 through 10, inclusive, illustrate sequentially the steps entailed in the practice of the novel method disclosed herein for manufacturing the tube envelopes.

While the invention is susceptible of various modifications and alternative constructions, a preferred embodiment and method have been illustrated in the drawings and will be described below in considerable detail. It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the intention is to cover all modifications and alternative constructions falling within the spirit and scope of the invention as expressed in the appended claims.

Referring more specifically to the drawing, there is shown in Figures 1 and 2 an illustrative tube envelope T embodying the present invention. The illustrative envelope comprises a ground and polished viewing screen panel or window panel 20 of substantially uniform thickness, a funnel 21 and a neck 22, all welded together into an integral unit. The panel 20 is preferably fashioned from a somewhat convex piece of plate glass and bulges outwardly from the funnel 21. In the present instance, the latter is a pressed glass member of general conical shape and at its base or larger end it is welded to the marginal edge portion of the inner face of the window panel. On the outside of the tube envelope, a heavy peripheral head 25 is formed in surrounding relation to the paneland the base of the funnel at the region of juncture between these members. As indicated in the drawing, the bead 25 is of laterally convex contour and is defined by a thickened portion of the funnel wall together with the rounded outer peripheral portion of the panel 20. Inside the tube envelope T there is formed a relatively small fillet 26 which gently merges into the inner surfaces of both the panel and the funnel.

Turning now to the novel method whereby the tube envelope T is constructed, it should be noted that such method entails the welding of a window panel blank 20A to a funnel blank 21A (refer to Fig. 4). In this connection, I have discovered that the envelope T as described herein cannot be constructed satisfactorily unless the transverse dimension or diameter of the peripheral edge of the window panel blank exceeds the corresponding external transverse dimension or diameter of the base of the funnel blank so as to define a substantial marginal overlap M on the inner face of the panel blank. While such overlap may vary depending upon the particular thicknesses of the glass used for the panel and the funnel, I have found, for example, that a minimum of approx:-

mately is required on a diameter tube envelope, the-maximum being about equal to the panelthickness.

Starting with the panel and funnel blanks 20A and 21A as indicated in Fig. 4, the first step in the practice of the :method' of .the present invention is to preheat these" blanks ma furnace, 'stoppingwell short of their fusion tempera- :ture. .Forsoda lime and leadglasses, asatisfactory. preheat temperature might well be found inthe range "of frorn 4l0 .to 425. F.

.Once the. blanks have been preheated; the next step is to mount them in axially spaced relation upon arr appropriate rotatablesupporting device-which is adapted to rotate them inv unisonyabout. a common axis. The rotatable supporting-device should. also include provision for movlngand adjustably positioning'thej blanks axially .r'ela -tive to each other.

Referring to Fig. 5,.aszthe preheated blanks:20A,z2lA are rotated, heat is first applied to :theperipheral edge of the panel by. means. of: one or-more burners .129. which produce'ahighly concentrated and extremelyhigh temperature .flarne. The panel blank is heated individually first because in practically. every instancesit is made of thicker glass than the funnel blank for structural reasons and consequently takes more-heat to;bring its fusion area upto proper welding temperature. When :the peripheral edge portionof the panel. blank 20A.has reached. fusion temperature, the. glass therein willzbecome plasticand will tend tov assume a rounded off shape due tosithe asurface tension action. When this occurs, the panel and. the funnel blanks are moved axially relative-to.each-other and into closely spaced relation; still rotating in unison. The flame from the burner 29 is then applied to the'end of the funnel blank 21A as well as the peripheral edge of the panel blank 20A as. shown :in Fig. 6. Thisaction is continued for a predetermined time until theedge portion of the funnel blank 21A facing the.- panel blank, also reaches the plastic state whereupon it rounds offas indicated in Fig. 7. Whenthis occurs, the rotating-panel and funnel blanks are moved axially relative to .one another through a short distance andare brought firmlyinto contact with each other. Relative axial" movement between these members, as well as movement oftheburner 29 axially thereof, is maintained for a predetermined period of time. In the present instance, it has been found convenient to accomplish the foregoing step by holding the funnel blank fast while reciprocating the panel blank and the burner 29 in unison, as shown in Fig. 8. Such action produces a working of the plastic glass'of'thepanel and of the funnel, facilitating the tendency of the surface tension of these glasses to produce smooth inner and outer surfaces at the fusion region. The working action indicated in Fig. 8 continues until the wall thickness in the fusion region at least equals and preferably exceeds the thickness of the glass in the funnel. By this time the outer peripheral bead 25 has built up to a considerable size although it will probably have a central groove therein. To facilitate the smoothing out of the peripheral bead 25, the working action of the fused panel and funnel is stopped and the burner 29 reciprocated axially over the bead as shown in Fig. 9 while the panel and funnel rotate in unison thereunder. This effects a glazing or smoothing action due to glass flow induced by surface tension and thereby eliminates the groove in the bead, producing a smoothly curved, laterally convex surface thereon.

When the foregoing has been accomplished, the stresses induced in the panel and funnel as a result of the fusion operation are distributed and-equalized by rotating the newly formed-envelope relative :toa pair of annealing burners 3%, as indicated in Fig. 10. The latter are arranged to direct a widelydistributed and relatively low temperature flame upon a wide area on either side of'the fusion region. Upon completion of this initial annealing operation, rotation of the newly formed tube envelope is stopped and the envelope is removed from the rotatable supporting device, whereupon it is immediately placed in a lchr or annealing furnace and brought down to a safe temperature at a gradual rate.

As an incident to the foregoing operation, it mightbe noted in passing that fusion between the panel and funnel members occurs along asubstantially uniform and reversely curved annular abutment area 31 between the inner face of the panel and the end of the funnel base. The surface 31 becomes readily detectable when glasses of different composition are:us.ed forthe panel and. for the funnel,

A common requirement for cathode ray tubes used in .4 television rceeiving sets is that each such tube must be -ableto-withstandan-external'pressure of 60-pounds-per square inch absolute. Tubes embodying the novel construction described above are capable of easily withstanding such test and, as a matter of fact, will withstand substantially more external pressure without breakage. Consequently, such construction -is.particularly well adapted for, tubesshavingdiameters, between 10 and, 20 inches. Variations in" tubediameter ofcourse-necessitate corresponding variationsin panel. and. funnel thicknesses.

While .a mathematical analysis ,ofv the internal stresses in the tube envelope T will serve to bear out, the, strength inherent in its construction, it has been experimentally determinedothatysuch; strength -resides primarily ,in the peripheral bead surrounding the adjoining portions of the panel and the funnel. ILhas. also been determined experimentally that this bead is not obtainable without the marginal overlap M between the panel and the funnel as indicated in Fig. 4. ;Thus-,-whcn,the diameter of thepanel .and the external diameter of :the :funnel areidentical and .thezparts areafusedntogether, ;the;-peripheral bead is non- .ex-istent. .Such:. a tube-envelope has:been found utterly incapable of withstanding ,the pressure :test outlined above and is consequently ,-unsati sfa ctorylfor.:commercial use. Further evidence ofthe; importance of the peripheral bead cannbe found-by eccentrically fusing,- a;.panel blank to a funnel blank so-thanthere-is marginaloverlap onone side only. The peripheral bead consequently forms only -'.where there is marginal overlap. :When a tube envelope so; constructed 5 is; subjected to, the; pressure .test, it always fails at the nonfoverlapped side where there is-noperipheralrbead.

.VTubes. constructed in accordance with the .present invention possess.tsuflieientz strength to. permit the use. of

' different, glassesginathepaneland; funnel, regardless of whether'orxnotz they possess the same. .coeflicient of expansion. The only limitation. istthat the internal stress due to a differencedn. expansionbe held to approximately 100kilogramspersquarecentimeter. r In other words, in glasses having. a ,coeflicient of expansion 'in the vicinity'of X10-'lper C.,-,the maximum difference-of coefficient shouldbe about 5. Itlis, however, preferable to construct the. tube envelope with either the, same coefficientsof expansion in the.panel; and the funnel orta -slightlyhigher coefiicient-ofexpansion in, the panel than in the funnel. In'the: latter; instance, the envelope: derives: additional reinforcement .due to, the fact that the: panelrbehaves somewhat as a barrelhoop insofar; as, the funnel. is concerned.

;It willnow beappreciated that tube, envelopesembodyingxthe present invention: possessa number of important advantages. .For example, such. envelopes'are substantiallylighter. fortthe same strength ithanglass tube envelopesoficomparable sizein useheretofore. ,The window panel of theenvelopeT has highoptical qualities, possessing substantiallymore viewing area. than previously known tubesand-being viewable .;throughout a wider. angle, than such: tubes. The :ground; and polished surfaces on the inside and the. outsidezofthe panel,.togetherwith its uniform .1thickness,,, contribute substantially to this. The smooth inside; surface; of rthe-panelis: also mportant from atube manufacturing standpointtbecause it virtually eliminates the possibility .of having defects iappear :after: the fluorescent coatinggisr applied to the, ;inner surface. This means thatz rnanufacturing: losses ;in.;the; final; steps of assembling the;tube;.are:.considerably educed. gThehigh strength of thertuberenvelope gis. alsoesignificantjtfrom the standpoint of. safetysince ritarlargely; eliminatesithe possibilityoftbreakageiof theztube whenrinstalled; in aitelevision receiving set.

: I claimas mytinvention:

1.21m the-manufacture :Of'iEIlVElOPflSf for electron;. .dischargeatubes; theemethod'tof effecting ta seal: between a ground andvpolishediwindow .panelaof substantiallyc uniform "thicknessand the larger end-tportiontof; a glass funnel member, said method comprising the steps of forming said window -panel=:with-- a transverse dimension' in excess of the corresponding outer-transverse dimension:of the largerend of said funnelby an amount-not exceeding twice the thickness of said panel,preheatingsaidpanel and saidfunnelto a temperature below their ifusion point, placing one face of- ,s'aidpan'el, andzsaid larger end of the funnel in closely spaced relation; bringing the=juxtaposed edgesof saidj funnel and said panel .to their fusion temperature bythe application of, heat: from an appropriate source, said panel and said funnel being relativelyrotatable with respect to the heat source, bringing said juxtaposed edges of said panel and said funnel into contact, reciprocating said panel and said funnel relative to each other without breaking such contact while at the same time reciprocating the heat source relative thereto, stopping said relative reciprocation of said panel and said funnel while continuing the reciprocation of said heat source relative thereto so as to eifect a glazing operation, removing said heat source from the fusion area between said panel and said funnel at the conclusion of the glazing operation, and annealing said fused panel and funnel.

2. In the manufacture of envelopes for electron discharge tubes, the method of making a seal between the larger end portion of a glass funnel member and a ground and polished window panel of concave-convex form and substantially uniform thickness, said method comprising the steps of forming said window panel with a transverse dimension in excess of the corresponding outer transverse dimension of the larger end of said funnel by an amount not exceeding twice the thickness of said panel, preheating said panel and said funnel to a temperature below their fusion point, placing the larger end of said funnel in closely spaced and coaxial relation with the marginal edge portion of the concave face of said panel, bringing the juxtaposed portions of said funnel and said panel to their fusion temperature by the application of heat from a first heating means, said panel and said funnel being mounted for rotation relative to said first heating means, bringing said juxtaposed portions of said panel and said funnel into contact while rotating said panel and said funnel relative to said first heating means, reciprocating said panel and said funnel relative to each other without breaking said contact so as to create a relatively heavy peripheral bead around the fused portions of said panel and said funnel, said first heating means being reciprocated relative to said funnel and said panel at the same time, stopping the relative reciprocation of said panel and said funnel while continuing the reciprocation of said first heating means relative thereto so as to make said peripheral bead laterally convex, removing said first heating means from the region of the peripheral bead, annealing said fused panel and funnel by the application of heat from a second heating means, and lehring said fused panel and funnel.

3. In the manufacture of cathode ray tube envelopes for television equipment and the like, the method of eifecting a seal between a plate glass window panel of concaveconvex shape and the larger end portion of a generally frusto-conical glass funnel member, said method comprising the steps of dimensioning the window panel and the larger end portion of the funnel so as to create a substantially uniform marginal overlap not in excess of the thickness of the panel when the same is brought into abutting relation with the larger end of the funnel, preheating said panel and said funnel to a temperature within the range of 410 to 425 F., mounting said funnel and said panel coaxially with the larger end of the funnel in closely spaced relation with the marginal edge portion of the concave face of said panel, rotating said funnel and said panel at a common speed, applying heat to the peripheral edge portion of said panel from a first heat source until said peripheral edge portion reaches its fusion temperature, applying heat to the larger end portion of said funnel from said first heat source until said larger end portion reaches its fusion temperature, said first heat source also maintaining said peripheral edge portion of the panel at fusion temperature, bringing the juxtaposed portions of said panel and said funnel into contact while continuing rotation of the same and application of heat thereto from said first heat source, reciprocating said panel and said funnel relative to each other Without breaking said contact and while continuing to rotate the same so as to build up a relatively heavy peripheral bead surrounding the region of fusion and a relatively small fillet between said concave face of said panel and the inside surface of said funnel, said first heat source being recip rocated relative to said panel and said funnel at the same time, stopping the relative reciprocation between said panel and said funnel while continuing the rotation thereof and also while continuing the reciprocation of said first heat source until said peripheral bead acquires a relatively smooth laterally convex surface, removing said first heat source, annealing by means of a second heat source said fused panel and funnel while continuing rotation of the same, stopping rotation of said fused panel and funnel, removing said second heat source, and placing said fused panel and funnel in a lehr.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,548,611 Kearsley et al. Aug. 4, 1925 2,132,783 Goldmark Oct. 11, 1938 2,160,081 Niclassen May 30, 1939 2,160,434 Harris May 30, 1939 2,222,197 Engels Nov. 19, 1940 2,232,322 Gilmore Feb. 18, 1941 2,240,352 Schmidt Apr. 29, 1941 2,264,183 Nash Nov. 25, 1941 2,320,946 Madden June 1, 1943 2,359,500 White Oct. 3, 1944 2,362,171 Swanson Nov. 7, 1944 2,413,338 Small Dec. 31, 1946 FOREIGN PATENTS Nu er Country Date 851,808 France Mar. 18, 1939 536,858 Great Britain May 29, 1941 

